The problem of how to dispose of used vehicle tires has for many years been a major environmental concern. In particular, the U.S., as the major world consumer of automobiles and trucks, discards millions of worn-out tires every year. As an economical disposal method has not been found to date, huge unsightly piles of used tires are commonplace. These large piles of tires present a significant fire hazard, as the tires readily ignite and continue to burn without assistance. Furthermore, large piles of discarded tires present a serious health endangerment threat, as standing pools of water within the tires provide ideal breeding grounds for disease-carrying mosquitos.
A significant amount of research has been done to try to solve the problem of disposing of used tires. Governments, such as in the U.S., have for some time applied a levy on the disposal of tires in order to sponsor such research. One process involves reclaiming the rubber from within the tires by the treatment of ground vulcanized scrap tires and other miscellaneous rubber articles with heat and chemical agents. Broadly, the reclaiming process involves first grinding the scrap rubber, then applying a heat treatment for depolymerization and finally processing with intensive friction milling. Unfortunately, this reclamation process is relatively expenses per tire and thus has not seen large scale implementation.
In U.S. Pat. No. 4,648,328 to Keough, a process in which used tires are subjected to a destructive distillation inside a pyrolysis chamber is shown. First, the tire fragments are shredded and then the tire is subjected to temperatures between 800.degree. and 1600.degree. F. in an oxygen-free atmosphere. The gaseous by-products are removed and oil separated therefrom while the solid components are directed to a series of devices for separating the steel, glass fibers, and carbon black. Another effort at disposing of used tires utilizing a destructive distillation device is shown in U.S. Pat. No. 4,613,408 to Howard.
A more cost effective means for disposing of used tires has been incineration to produce energy. Two examples of these efforts are shown in U.S. Pat. No. 4,846,082 to Marangoni, and Japanese Patent No. 55-65820 to Noboru. U.S. Pat. No. 5,101,739 to Nance, et al., discloses burning tires at relatively low heat to produce usable fuel gas. A tire disposal system which utilizes the heat generated from initial combustion in a co-generation facility is shown in U.S. Pat. No. 4,895,083 to McDilda. In this system, the optimum burning temperature is between 2300.degree. and 2500.degree. F. The emissions from the combustion travel through a tortuous series of baffles and filters to capture any carbon black therein. A drawback of this system is the high energy input required to completely combust the tires. Moreover, environmental pollution standards have become increasingly stringent, mandating the addition of more effective effluent gas filters or scrubbers.
In general, because of the high cost of pollution reduction equipment, in combination with the relatively low BTU content of the used tires, incineration to produce usable heat has only proved economically viable when implemented on a large scale in areas where a steady stream of tires is guaranteed, such as proximate urban centers. Unfortunately, there is significant resistance to construction of such tire burning plants near densely populated areas. Further, there has been a problem with some systems which burn tires in an incomplete combustion reaction to obtain fuel gas. Specifically, the amount of contaminants in the fuel gas leads to serious compressor clogging and buildup of sludge in containment tanks or bladders.
Thus, there has been a need for a more efficient, clean and cost effective system for disposing of used tires.